This invention relates to an epoxy resin composition that is good in curability and shelf life and is useful in the field of electronic and electric materials, and to a semiconductor device obtained by using said composition.
Electronic and electric materials, in particular, IC encapsulating materials, have recently been required to have not only a rapid-curability for improvement in production efficiency but also an improved shelf life for improvement in handleability at the time of transportation and storage. In epoxy resin compositions for use in the electronic and electric field, various compounds, for example, phosphines, amines, nitrogen-containing heterocyclic compounds such as imidazole type compounds and diazabicycloundecene, quaternary ammonium, phosphonium and arsonium compounds have been used as curing accelerators.
These conventional curing accelerators often have curing-accelerating effect also at a relatively low temperature such as ordinary temperature. This property deteriorates the quality of a product, for example, it causes viscosity increase, fluidity decrease, nonuniformity in curability, etc. during the production of an epoxy resin composition and the storage of the resulting epoxy resin composition. In order to solve this problem, the so-called latent curing accelerators capable of suppressing viscosity and fluidity changes with time at low temperatures and causing curing reaction only on heating at the time of shaping or molding have been vigorously investigated in recent years. As a means for solving the problem, the impartment of the latency by protecting the active site of a curing accelerator with an ion pair is investigated. JP-A-8-41290 discloses latent curing accelerators having a salt structure formed by each of various organic acids and a phosphonium ion. This phosphonium salt, however, does not have a specific high-order molecular structure, so that the ion pair is relatively easily affected by the external environment. Therefore, recent semiconductor-encapsulating materials obtained by the use of low-molecular weight epoxy resins or phenol-aralkyl resins are disadvantageous in that they have a deteriorated shelf life.
The present invention is intended to provide an epoxy resin composition that has both a rapid-curability and an excellent storage stability and is useful in the field of electronic and electric materials, and a semiconductor device obtained by using said composition.
That is, the present invention provides an epoxy resin composition comprising a compound (A) having two or more epoxy groups in the molecule, a co-condensation product (B) having two or more phenolic hydroxyl groups in the molecule, and a molecular association product (C) of a tetra-substituted phosphonium (X), a compound (Y) having two or more phenolic hydroxyl groups in the molecule, and a conjugate base of the compound (Y) having two or more phenolic hydroxyl groups in the molecule, said conjugate base being a phenoxide type compound obtained by removing a hydrogen atom from the aforesaid compound (Y) having two or more phenolic hydroxyl groups in the molecule; and a semiconductor device characterized by being obtained by encapsulating a semiconductor element with said composition. The present inventors found that an epoxy resin composition having very excellent curability and storage stability can be obtained by utilizing a salt structure having a protected reactive site, as a curing accelerator, whereby the present invention has been accomplished.